(1) Field of the Invention
The present invention relates generally to switch assemblies, and more particularly to a switch assembly that can protect a delicate switch such as a reed switch from shock and vibration loads.
(2) Description of the Prior Art
Proximity switches are typically used to detect the presence or passage of an object. One type of proximity switch is the reed switch in which metallic strips (or reeds as they are known) are hermetically sealed in an elongate, air or gas-filled glass body. Each reed is connected to an electrical lead that passes out of the glass body at either end thereof. When a magnetic body is brought near a reed switch, magnetic forces cause overlapping portions of the reeds to contact one another thereby closing a circuit to which the electrical leads are connected.
The Navy uses such reed switches in various submarine launch systems to indicate launch tube and hatch valve positions. To protect the delicate glass bodies of the switches, they are epoxied to a housing and the housing is glued to a foundation. The assembly is then encapsulated in urethane. However, the switches' glass bodies have still been known to crack or break when experiencing shock or vibration loads. Further proper positioning of a reed switch on a platform is critical to its effective operation. Unfortunately, the method of simply gluing the housing in place makes proper positioning of the switch a skilled operation or simply leaves it to chance.
A variety of protective housing structures for reed switches have been developed. For example, U.S. Pat. Nos. 3,167,625 and 3,701,960 disclose mounting structures in which a glass reed switch is held in air within a spool-like frame by means of elastic collars or buffers. Wires connect to the terminals on the reed switch with the connections being subject to strain forces. Further, since the glass body of the reed switch is only supported at the collars or buffers, shock and vibration loads are focused at these few locations thereby increasing the chance that the glass body will fracture. U.S. Pat. No. 3,958,199 discloses a reed switch that is fully encapsulated in polyurethane. While this design tends to better damp out shock and vibration loads, proper and consistent positioning of the reed switch in the encapsulant during the manufacturing thereof is difficult to achieve.